Sympathy walkouts in support of 647 sacked construction workers at Lindsey refinery more than doubled today, reaching the Sellafield nuclear power complex and a biofuel plant on Teesside.

The unofficial protests came as the men at the centre of the 10-day-old dispute burned their letters of dismissal and were joined in a mass protest by colleagues from the neighbouring Conoco refinery at Immingham on Humberside.

Neither side gave any ground over the key issue of 51 redundancies at Lindsey at a time when 61 new jobs have been offered to other men and several hundred Portuguese and Italian workers are still on site.

The sacked men were at the centre of unofficial action in January and February over the alleged denial of jobs to British building workers when the foreign recruits were shipped in and housed on a barge in Grimsby docks.

The French company Total, whose new £200m hydro desulphurisation plant at Lindsey has been hit by the disputes, repeated its refusal to talk until the strikers reapplied for their jobs. The firm claimed that contractors employing the steel erectors, platers and electricians had received an "encouraging" response from staff, but strikers said no one was "crawling back in on their bellies for jobs".

Commenting on the dispute, Gordon Brown said: "This is a matter between the management and workers, but we would hope it can be resolved as quickly as possible. It continues to be our view that the parties do need to talk, ideally through Acas."

The unions Unite and the GMB, which plan a big demonstration outside the refinery early on Wednesday if no progress is made, repeated their request for direct talks.

More than 3,000 workers downed tools at other building sites in the energy sector during the day, with 900 walking out at Sellafield, 600 at South Hook, Dragon and Aberthaw in Wales and 200 at Drax and Eggborough power stations between Hull and Leeds. Another 1,000 left the Ensus biofuel plant on Teesside.

A sacked worker, Kenny Ward, a GMB steward, told a meeting of strikers outside the refinery front gate: "Would Total do this in France? Absolutely not. The French wouldn't put up with it – or the French government, or the German government, or the Spanish, the Italians and every other government in the European Union. But our government will. We won't."

Total said it hoped to restart building work at the refinery within weeks – other operations there had not been affected. Power generation was not disrupted at any of the sites where workers had walked out in sympathy.

Total said in a statement: "We stress that at no stage have we asked contract companies to reduce their workforce's pay and conditions in any way and will not seek to do so. Total calls for all parties to respect employment law and to work together within the nationally negotiated agreements to which they are signatories."

Michel Benezit, Total's president of refining and marketing, said the dispute involved sub-contractors and was out of the hands of the firm, which has been at Immingham for 40 years.

"The work should have been finished by now and the unit should be in operation. Because of poor productivity and disputes, we still have a long way to go," he said.

" I want to make it clear that we have not fired anyone, because we have no employees involved in this work. There is not much we can do. My only goal is to see an end to the strike as soon as possible."

Gary Stockton, senior organiser for the Unite union at Sellafield, said welders, electricians, platers and pipe fitters had decided to all walk out until Wednesday after a mass meeting this morning as part of a "sympathy stoppage" with workers at the Lindsey refinery. "We are in the campaign together, we work together," he said. "This has got nothing to do with the way we are treated at Sellafield – Sellafield do everything by the book. It's the way the 51 lads were treated at Lindsey. You have got this company thinking they can ride roughshod over the men."